Re: [Qemu-devel] [RFC for-2.7 1/1] block/qapi: Add query-block-node-tree

[Wen Congyang <wency@cn.fujitsu.com>]

On 03/25/2016 03:07 AM, Max Reitz wrote:
> This command returns the tree of BlockDriverStates under a given root
> node.
> 
> Every tree node is described by its node name and the connection of a
> parent node to its children additionally contains the role the child
> assumes.
> 
> A node's name can then be used e.g. in conjunction with
> query-named-block-nodes to get more information about the node.

I found another problem:

{'execute': 'query-block-node-tree', 'arguments': {'root-node': 'disk1' } }
{"return": {"children": [{"role": "children.1", "node": {"children": [{"role": "file", "node": {}}], "node-name": "test1"}}, {"role": "children.0", "node": {"children": [{"role": "file", "node": {}}]}}]}}

s->children[0] is children.0, and s->children[1] is children.1.
But we output them in reverse order. The reason is:

BdrvChild *bdrv_attach_child(BlockDriverState *parent_bs,
                             BlockDriverState *child_bs,
                             const char *child_name,
                             const BdrvChildRole *child_role)
{
    BdrvChild *child = bdrv_root_attach_child(child_bs, child_name, child_role);
    QLIST_INSERT_HEAD(&parent_bs->children, child, next);
    return child;
}

We insert the new child to the head, not the tail...

Thanks
Wen Congyang

> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  block/qapi.c         | 43 +++++++++++++++++++++++++++++++++++++++++++
>  qapi/block-core.json | 46 ++++++++++++++++++++++++++++++++++++++++++++++
>  qmp-commands.hx      | 38 ++++++++++++++++++++++++++++++++++++++
>  3 files changed, 127 insertions(+)
> 
> diff --git a/block/qapi.c b/block/qapi.c
> index 6a4869a..a35d32b 100644
> --- a/block/qapi.c
> +++ b/block/qapi.c
> @@ -493,6 +493,49 @@ BlockInfoList *qmp_query_block(Error **errp)
>      return head;
>  }
>  
> +static BlockNodeTreeNode *qmp_query_block_node_tree_by_bs(BlockDriverState *bs)
> +{
> +    BlockNodeTreeNode *bntn;
> +    BlockNodeTreeChildList **p_next;
> +    BdrvChild *child;
> +
> +    bntn = g_new0(BlockNodeTreeNode, 1);
> +
> +    bntn->node_name = g_strdup(bdrv_get_node_name(bs));
> +    bntn->has_node_name = bntn->node_name;
> +
> +    p_next = &bntn->children;
> +    QLIST_FOREACH(child, &bs->children, next) {
> +        BlockNodeTreeChild *bntc;
> +
> +        bntc = g_new(BlockNodeTreeChild, 1);
> +        *bntc = (BlockNodeTreeChild){
> +            .role = g_strdup(child->name),
> +            .node = qmp_query_block_node_tree_by_bs(child->bs),
> +        };
> +
> +        *p_next = g_new0(BlockNodeTreeChildList, 1);
> +        (*p_next)->value = bntc;
> +        p_next = &(*p_next)->next;
> +    }
> +
> +    *p_next = NULL;
> +    return bntn;
> +}
> +
> +BlockNodeTreeNode *qmp_query_block_node_tree(const char *root_node,
> +                                             Error **errp)
> +{
> +    BlockDriverState *bs;
> +
> +    bs = bdrv_lookup_bs(root_node, root_node, errp);
> +    if (!bs) {
> +        return NULL;
> +    }
> +
> +    return qmp_query_block_node_tree_by_bs(bs);
> +}
> +
>  static bool next_query_bds(BlockBackend **blk, BlockDriverState **bs,
>                             bool query_nodes)
>  {
> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index b1cf77d..754ccd6 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -470,6 +470,52 @@
>  
>  
>  ##
> +# @BlockNodeTreeNode:
> +#
> +# Describes a node in the block node graph.
> +#
> +# @node-name: If present, the node's name.
> +#
> +# @children:  List of the node's children.
> +#
> +# Since: 2.7
> +##
> +{ 'struct': 'BlockNodeTreeNode',
> +  'data': { '*node-name': 'str',
> +            'children': ['BlockNodeTreeChild'] } }
> +
> +##
> +# @BlockNodeTreeChild:
> +#
> +# Describes a child node in the block node graph.
> +#
> +# @role: Role the child assumes for its parent, e.g. "file" or "backing".
> +#
> +# @node: The child node's BlockNodeTreeNode structure.
> +#
> +# Since: 2.7
> +##
> +{ 'struct': 'BlockNodeTreeChild',
> +  'data': { 'role': 'str',
> +            'node': 'BlockNodeTreeNode' } }
> +
> +##
> +# @query-block-node-tree:
> +#
> +# Queries the tree of nodes under a given node in the block graph.
> +#
> +# @root-node: Node name or device name of the tree's root node.
> +#
> +# Returns: The root node's BlockNodeTreeNode structure.
> +#
> +# Since: 2.7
> +##
> +{ 'command': 'query-block-node-tree',
> +  'data': { 'root-node': 'str' },
> +  'returns': 'BlockNodeTreeNode' }
> +
> +
> +##
>  # @BlockDeviceTimedStats:
>  #
>  # Statistics of a block device during a given interval of time.
> diff --git a/qmp-commands.hx b/qmp-commands.hx
> index 9e05365..5c404aa 100644
> --- a/qmp-commands.hx
> +++ b/qmp-commands.hx
> @@ -2637,6 +2637,44 @@ EQMP
>      },
>  
>  SQMP
> +query-block-node-tree
> +---------------------
> +
> +Queries the tree of nodes under a given node in the block graph.
> +
> +Arguments:
> +
> +- "root-node": Node name or device name of the tree's root node (json-string)
> +
> +The block node tree is represented with BlockNodeTreeNode and BlockNodeTreeChild
> +json-objects.
> +
> +Each BlockNodeTreeNode json-object contains the following:
> +
> +- "node-name": If present, the node's name (json-string, optional)
> +- "children": json-array of the node's children, each entry is a json-object of
> +              type BlockNodeTreeChild
> +
> +Each BlockNodeTreeChild json-object contains the following:
> +
> +- "role": Role the child node assumes for its parent, e.g. "file" or "backing"
> +          (json-string)
> +- "node": BlockNodeTreeNode describing the child node (json-object)
> +
> +The cyclic reference of BlockNodeTreeNode and BlockNodeTreeChild to each other
> +thus spawns a tree.
> +
> +This command returns the root node's BlockNodeTreeNode structure.
> +
> +EQMP
> +
> +    {
> +        .name       = "query-block-node-tree",
> +        .args_type  = "root-node:B",
> +        .mhandler.cmd_new = qmp_marshal_query_block_node_tree,
> +    },
> +
> +SQMP
>  query-blockstats
>  ----------------
>  
>